This thought has crossed my mind before, but IANAL so no answer from me.
But lets not mention morals in this thread.
I hate it when a great legal question gets shipped to GD just because of a few idiots.
I disagree. It’s your fault that he’s faced with the choice to either die or violate his deeply held beliefs. I think you’d be criminally liable. However, if the facts were that it was an accident and that you attempted to help afterwards, you would probably be found guilty of, at most, a lower form of manslaughter. If you show real contrition, you might not serve any time at all.
IANAL and I don’t know the answer to the OP, but I’ll present a similar situation which is much more likely to have precedents. Say you were responsible for a serious injury, the victim’s family signs a DNR (do not recuscitate), and the patient dies. If you were charged in this case, it would set a precedent that some medical treatment could be skipped without alleviating the responsibility of the original assailant.
My opinion is worth what you paid for it, but I think you’re responsible in either case.